The Annual Reproductive Cycle of the Sipunculid Phascolosoma agassizii

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Abstract
Phascolosoma agassizii. a sipunculid common on the West Coast of North America, and sampled at Monterey, California was found to contain gametes much of the year in the samples collected monthly. However, the eggs appearing soon after the large spawning period were small and increased in diameter with time, more and more eggs of large diameter appearing in the body fluid until only large eggs were present. The eggs then entered in the nephridia preparatory to spawning in March. Few eggs were seen in April, May and June of 1961, many small eggs being present in July. In males, sperm balls are present in the body fluid and they also enter the nephridia preparatory to spawning. The gametic mass (obtained by centrifugation) may constitute as much as 37% of the dry mass of the tissues (exclusive of serum), but it is generally less than 30%. The gametic mass was found to be less in males than in females. The breeding cycle in this species is compared to that of other sipunculids.